1. Field of Invention
This invention relates to a method for fabricating a trench isolation structure.
2. Description of Related Art
The device isolation structures formed in advanced semiconductor processes are mostly trench structures. A trench structure is conventionally formed by forming a trench in a substrate and then forming an insulating layer filling up the trench by HDP-CVD or the spin-on dielectric (SOD) technique.
However, when the process linewidth is reduced to below 20 nm and the aspect ratio of the trench is larger than 6, a void is easily formed in the insulating layer filled in the trench. Such a void seriously affects the device reliability and the yield, and also hinders the miniaturization of the semiconductor device geometry. For example, a contact later formed over the trench isolation with an opened void in the insulating layer may cause punch-through to the isolated area.